Majority Of Colon Tumors Research Articles

Rapidly cycling Lgr5+ stem cells are exquisitely sensitive to extrinsic dietary factors that modulate colon cancer risk.

The majority of colon tumors are driven by aberrant Wnt signaling in intestinal stem cells, which mediates an efficient route toward initiating intestinal cancer. Natural lipophilic polyphenols and long-chain polyunsaturated fatty acids (PUFAs) generally suppress Wnt- and NF-κB- (nuclear factor-κ light-chain enhancer of activated B-cell) related pathways. However, the effects of these extrinsic agents on colonic leucine-rich repeat-containing G-protein-coupled receptor 5-positive (Lgr5+) stem cells, the cells of origin of colon cancer, have not been documented to date. Therefore, we examined the effect of n-3 PUFA and polyphenol (curcumin) combination on Lgr5+ stem cells during tumor initiation and progression in the colon compared with an n-6 PUFA-enriched control diet. Lgr5-EGFP-IRES-creERT2 knock-in mice were fed diets containing n-6 PUFA (control), n-3 PUFA, n-6 PUFA+curcumin or n-3 PUFA+curcumin for 3 weeks, followed by 6 azoxymethane (AOM) injections, and terminated 17 weeks after the last injection. To further elucidate the effects of the dietary bioactives at the tumor initiation stage, Lgr5+ stem cells were also assessed at 12 and 24 h post AOM injection. Only n-3 PUFA+curcumin feeding reduced nuclear β-catenin in aberrant crypt foci (by threefold) compared with control at the progression time point. n-3 PUFA+curcumin synergistically increased targeted apoptosis in DNA-damaged Lgr5+ stem cells by 4.5-fold compared with control at 12 h and maximally reduced damaged Lgr5+ stem cells at 24 h, down to the level observed in saline-treated mice. Finally, RNAseq analysis indicated that p53 signaling in Lgr5+ stem cells from mice exposed to AOM was uniquely upregulated only following n-3 PUFA+curcumin cotreatment. These novel findings demonstrate that Lgr5+ stem cells are uniquely responsive to external dietary cues following the induction of DNA damage, providing a therapeutic strategy for eliminating damaged Lgr5+ stem cells to reduce colon cancer initiation.

Abstract 229: A metabolic switch controls cell fate decision-making in intestinal differentiation downstream of the tumor suppressor adenomatous polyposis coli (apc)

Abstract Mutation in the tumor suppressor Adenomatous Polyposis Coli (APC) is the primary initiating mutation in a majority of colon tumors. Recent studies have shown that APC positively correlates with Mitochondrial Pyruvate Carrier 1 (MPC1), a crucial player in pyruvate metabolism and has been reported to repress the Warburg effect and growth in colon cancer cells. Utilizing the zebrafish to examine the relationship between apc and mpc1, we found that mpc1 expression is reduced in embryos harboring a genetic mutation (apcmcr) or diminished expression (apc mo) of apc. Antisense morpholino knockdown of mpc1 in wild type embryos (mpc1 mo) resulted in an array of developmental defects that recapitulated phenotypes of impaired apc function including failed intestinal differentiation. This was accompanied by mitochondrial dysfunction in mpc1 mo as evidenced by a decrease in metabolic respiration and triglyceride levels. We also observed altered mitochondrial function and dysregulation of enzymes involved in pyruvate metabolism in apcmcr and apc mo. Moreover, hMPC1 RNA rescued intestinal differentiation in both zebrafish models of apc deficiency. Meta-analyses using TCGA human tumor samples corroborated our findings in the zebrafish. Our data demonstrate a novel role for apc in pyruvate metabolism through regulation of mpc1 that drives normal intestinal differentiation and support the broader idea that metabolic changes can dictate cell fate programs. Citation Format: Imelda T. Sandoval, Richard Glenn C. Delacruz, Braden N. Miller, Christeena Satterfield, Kristophor Olson, Shauna Hill, Holly Van Remmen, Jared Rutter, David A. Jones. A metabolic switch controls cell fate decision-making in intestinal differentiation downstream of the tumor suppressor adenomatous polyposis coli (apc). [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 229.

Chemoprotective natural compounds targeting DNA damaged stem cells‐ the cells of origin of colon cancer

The majority of colon tumors are triggered by aberrant Wnt signaling in intestinal stem cells, which is an extremely efficient route towards initiating intestinal cancer. Curcumin, a component of turmeric, and n‐3 polyunsaturated fatty acids (PUFAs), mainly found in fish oil, exert chemoprotective and anti‐inflammatory properties in part by modulating apoptotic, Wnt, and/or NFkappaB related pathways. However, the chemoprotective effects of diet on colonic adult stem cells‐the cells of origin of colon cancer are unknown. Therefore, we determined whether the combination of fish oil (FO) and curcumin (C) reduce colon cancer risk by modulating targeted apoptosis, DNA damage repair and proliferation in colonic Lgr5+ stem cells at the initiation stage of cancer compared to corn oil (CO, control) by utilizing Lgr5‐EGFP‐IRES‐creERT2 knock‐in mice fed diets containing CO±C or FO±C for 3 weeks followed by carcinogen (azoxymethane) injection. Interestingly, FO+C combination synergistically increased apoptosis (TUNEL) by 5‐fold, and promoted targeted DNA repair (MGMT+) by 9‐fold in DNA damaged (gamma H2AX+) stem cells compared to control. In general, stem cells were more responsive to environmental (carcinogen & diet) cues compared to non‐stem cells. These novel results demonstrate the unique ability of colonic stem cells to respond to external cues.

Effects of chemoprotective diets on crypt adult stem cells û the cells of origin of colon cancer (819.1)

The majority of colon tumors are triggered by aberrant Wnt signaling in intestinal stem cells, which is an extremely efficient route towards initiating intestinal cancer. Curcumin, a component of turmeric, and n‐3 polyunsaturated fatty acids (PUFAs), mainly found in fish oil, exert chemoprotective and anti‐inflammatory properties in part by modulating apoptotic, Wnt, and/or NFκB related pathways. However, the effects of diet on colonic stem cells are unknown. Therefore, we determined whether the combination of fish oil and curcumin reduced colon cancer risk by promoting targeted apoptosis of damaged colonic stem cells at the initiation stage of cancer. Lgr5‐EGFP‐IRES‐creERT2 knock in mice (n=10 per treatment) were fed diets containing corn oil ± curcumin (CO±C) or fish oil ± curcumin (FO±C) for 3 weeks. Apoptosis, cell proliferation and DNA damage in Lgr5+ stem cells were quantified 12 h post carcinogen (azoxymethane) injection. Interestingly, mice fed FO diets exhibited 15% fewer stem cells per crypt and an enhanced resistance to DNA damage, with 52% fewer damaged stem cells. For those stem cells exhibiting DNA damage, FO feeding enhanced targeted apoptosis by 24% compared to CO diets. In contrast, curcumin had no significant effects on stem cell responses. These novel results demonstrate the chemoprotective ability of external dietary cues to impact intestinal stem cell responses following carcinogen exposure.

Organic anion transporting polypeptide 1B3 (OATP1B3) is overexpressed in colorectal tumors and is a predictor of clinical outcome

OATP1B3 is an organic anion transporting polypeptide (OATP) that functions as a multispecific transporter in the normal liver. We examined the expression and clinical significance of OATP1B3 in colon cancers in tissue microarrays. Immunohistochemistry was used to assess OATP1B3 protein expression in paraffinized colon tumor tissue microarrays. OATP1B3 immunostaining was evaluated by location and intensity. Relationships between OATP1B3 expression, known prognostic variables and clinical outcomes were examined. 278 colon tumor samples of all stages were evaluated for OATP1B3 expression. OATP1B3 immunostaining was detectable in the majority (56%) of the tumor samples. Higher OATP1B3 expression was seen in lower stage tumors (p = 0.003) and lower grade (p = 0.004) tumors, but was not predictive of 5-year survival or tumor recurrence as an independent variable. Within individual tumor grades, OATP1B3 expression was associated with improved 5-year survival, but not recurrence in patients with poorly differentiated tumors. OATP1B3 expression was seen in the majority of colon tumors and may be a marker of lower grade and lower stage tumors and may predict for improved outcome in certain tumors.

Id2 Is a Target of the β-Catenin/T Cell Factor Pathway in Colon Carcinoma

Activation of beta-catenin/T cell factor (TCF) transcription as a result of mutations in the adenomatous polyposis coli (APC) and/or beta-catenin genes occurs in the majority of colon tumors. An increasing number of genes, including c-myc and cyclin D1, have been implicated as targets of this pathway. We now report that the dominant negative helix-loop-helix regulator Id2 is also a target of the beta-catenin/TCF transcription pathway in colon adenocarcinoma. Investigation of the mechanism for the overexpression of Id2 in colon carcinoma cells demonstrated that the Id2 promoter is activated, and the Id2 protein is up-regulated by beta-catenin. Conversely, reducing free beta-catenin blocked this induction of promoter activity. We have also used an electrophoretic mobility shift assay and supershift to identify a motif in the Id2 promoter that binds to TCF4 protein. Site-directed mutagenesis of this motif abolished promoter reporter activity. Both transfection of Id2 into SW480 cells and induction of Id2 in HT29 colon cells was found to increase anchorage-independent survival of these cells. Growing evidence associates disruption to Id2 expression with tumorigenesis, and our findings suggest that this dysregulation of Id2 expression is due to the activation of the beta-catenin/TCF pathway.

A locus that influences susceptibility to 1,2-dimethylhydrazine-induced colon tumors maps to the distal end of mouse chromosome 3

While inheritance of mutated alleles of highly penetrant tumor suppressor genes such as retinoblastoma or p53 predisposes individuals to a greatly increased risk of developing cancer, epidemiological data indicate that the majority of sporadic tumors in humans result from interactions of environmental and host genetic factors. The host genetic factors are poorly penetrant tumor susceptibility genes that determine the likelihood that a cancer will arise from carcinogen exposure. The majority of colon tumors in humans are sporadic in nature. 1,2-dimethylhydrazine (DMH)-induced colon tumors in mice provide a useful animal model to identify genes that influence susceptibility to carcinogen-induced colon tumors in humans. A genome-wide scan of genetic crosses of relatively sensitive C57BL/6J with relatively resistant CBA mice treated with DMH revealed a linkage of DMH susceptibility with the distal end of mouse chromosome 3, suggesting that one or more tumor susceptibility genes may map to this region.